1. Field of the Invention
The present invention relates to a method for power saving routing in wireless networks. Specifically, the invention relates to a new routing method which makes up for the weak points in conventional low power consumption routing methods by implementing gradual accessibility to a routing destination node with an optimum number of nodes participating in routing.
2. Background of the Invention
Development of wireless telecommunications and hardware design techniques has created a new paradigm of “mobile computing” by which users can communicate with each other using their portable devices irrespective of their physical locations. This mobile computing using mobile terminals has many restrictions such as non-connectivity, low bands, variability of high bands, connection with heterogeneous networks, security, low power, small storage space, etc. To overcome the shortage of power supply, one of the restrictions, a power adaption routing method that controls transmission power according to a distance between two nodes is used.
Many studies have been carried out on a routing method for finding an appropriate path in wireless network environments. Most of conventional routing methods are designed to minimize the number of nodes passed when a path is selected or delayed. This shortest distance methods is not suitable for an environment requiring minimum energy consumption.
Accordingly, a technique for efficiently reducing power consumption in a wireless environment where power consumption of a terminal is determined by its battery occupies an important position. Recently, routing methods for decreasing power consumption have been proposed. These methods reduce transmission power to decrease the radius electric waves can reach. That is, conventional methods shorten a transmission distance by passing by intermediate nodes to save power consumption on the basis of the fact that power consumption according to transmission in a wireless environment is proportional to constant multiplication of a distance between two transmission/reception terminals.
However, these conventional routing methods are not based on the number of optimum nodes for reducing power consumption but rather they execute an algorithm until a destination node is found by way of intermediate nodes for minimizing expected power consumption. Accordingly, many nodes may participate in routing and desert from the shortest distance to the destination node, increasing power consumption.
A conventional power consumption model and routing method are explained in more detail.
A model for a distance between two nodes and power consumption in a wireless environment includes RM model and HCB model. A general model of power consumed between two nodes having the distance d between them can be represented by the following equation (1).u(r)=arα+c  (1)where α, a and c are constants for indicating power consumed for purposes other than transmission and reception and the properties of wireless environment.
The equation (1) is represented by the equation (2) in RM model.u(d)=d4+2*108  (2)
According to Heizelman, Shandraksan and Balakrishnan, a terminal circuit consumes Eelec=50 nJ/bit in order to transmit/receive 1-bit radio data. When it is assumed that energy consumption according to energy transmission between two nodes having the distance d between them is proportional to a square of the distance d, a transmitting side consumes Eamp*d2(Eamp=100 pJ/bit/m2). Accordingly, transmitting and receiving sides respectively consume Eelec+Eamp*d2 and Eelec in order to transmit 1-bit data between the two nodes having the distance d between them. Where the two power consumption are divided by Eamp in order to normalize them, they can be represented by T=E+d2 (transmitting side) and P=E (receiving side). E is expressed as follows.E=Eelec/Eamp=(50 nJ/bit)/(100 pJ/bit/m2)=500 m2  (3)
Accordingly, power required for overall transmission and reception is represented by the following equation (4), which is called HCB model.u(d)=T+P=2E+d2  (4)
In the meantime, according to Stojmenovic and Xu Lin, direct transmission is a technique requiring minimum quantity of power in the case where a distance d between a source node and a destination node is d≦(c/a(1−21−α))1/α. On the other hand, in other environments where the distance d between the source node and destination node, d>(c/a(1−21−α))1/α, the method of dividing the distance between the two nodes by n (n is an integer close to d(a(α−1)/c)1/α) and transmitting data through nodes placed at divided points minimizes power consumption. The quantity of power consumption obtained by this technique can be represented by the following equation (5).                               v          ⁡                      (            d            )                          =                                            dc              ⁡                              (                                  a                  ⁢                                                                          ⁢                                                            α                      -                      1                                        c                                                  )                                                    1              α                                +                      d            ⁢                                                  ⁢                                          a                ⁡                                  (                                      a                    ⁢                                                                                  ⁢                                                                  α                        -                        1                                            c                                                        )                                                                              1                  -                  α                                α                                                                        (        5        )            
There was proposed a method for saving power consumption using the aforementioned equation as follows.
Referring to FIG. 2, to transmit data from a source node S to a destination node D via an intermediate node B, it is important to select the intermediate node B that minimizes expected power consumption. Here, r=|SB|, s=|BD| and d=|SD|.
Power Consumption needed for transmission between the node S and node B is u(r)=arα+c. When it is assumed that there are intermediate nodes for minimizing power consumption between the node B and node D, expected minimum power consumption can be predicted as follows.                               v          ⁡                      (            s            )                          =                              s            ⁢                                                  ⁢                                          c                ⁡                                  (                                      a                    ⁢                                                                                  ⁢                                                                  α                        -                        1                                            c                                                        )                                                            1                α                                              +                      s            ⁢                                                  ⁢                                          a                ⁡                                  (                                      a                    ⁢                                                                                  ⁢                                                                  α                        -                        1                                            c                                                        )                                                                              1                  -                  α                                α                                                                        (        6        )            
When α=2 in HCB model, the minimum power consumption is represented by the following equation (7).                               v          ⁡                      (            s            )                          =                  2          ⁢                                          ⁢                                    s              ⁡                              (                                  a                  ⁢                                                                          ⁢                  c                                )                                                    1              2                                                          (        7        )            
Accordingly, power consumption can be minimized by selecting the neighboring node B that minimizes the value of the equation (8).p(S,D)=u(r)+v(s)  (8)
Furthermore, in the case where there is a neighboring destination node, data can be transmitted to the destination node immediately to prevent routing from forming a loop.
In the above-described conventional method, however, the intermediate node was selected on the assumption that the nodes are ideally distributed at desired middle points between the node to be participated in routing and the destination node to minimize power consumption. Accordingly, power consumption between the intermediate node and destination node was expected to be v(s) as represented by the following equation (9).                               p          ⁡                      (                          S              ,              D                        )                          =                                            u              ⁡                              (                r                )                                      +                          v              ⁡                              (                s                )                                              =                                    2              ⁢              E                        +                          r              2                        +                          2              ⁢                                                s                  ⁡                                      (                                          a                      ⁢                                                                                          ⁢                      c                                        )                                                                    1                  2                                                                                        (        9        )            
That is, a factor that increases in proportion to a square of r and increases by a constant multiplication for d operates in FIG. 2. As shown in FIG. 3, accordingly, when value r′ is smaller than value r, node B′ is selected to become more distant from the destination node and gradual accessibility to the destination of routing may be lost.
Moreover, packets are continuously transmitted until the destination node is found. Accordingly, nodes more than the number of optimum nodes, which are participated in routing for saving power consumption, may participate in transmission. Furthermore, when the destination node exists at a neighboring node the packets are immediately sent to the destination node in order prevent formation of a loop, so that the optimum division value cannot be maintained. This may increase power consumption.